Update link to Oracle Linux

The https://linux.oracle.com/ url results in
too many redirects, which may result in our
link-checker to think the link is broken.

Replacing the link, per discussion in
https://github.com/docker/docker/pull/18534#issuecomment-164202592

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/installation/oracle.md

@@ -16,7 +16,7 @@ Support subscription to install Docker on Oracle Linux.
 This page instructs you to install using Docker-managed release packages and
 installation mechanisms. Using these packages ensures you get the latest release
 of Docker. If you wish to install using Oracle-managed packages, consult your
-[Oracle Linux documentation](https://linux.oracle.com).
+[Oracle Linux documentation](https://oracle.com/linux).
 
 
 ## Prerequisites